Center ring arrangement for a radial piston machine

ABSTRACT

The rotary cylinder block of a radial piston machine surrounds a control member whose outer surface has high pressure ports and low pressure ports communicating with the cylinders during rotation. The outer cylindrical surface of the control member also has a pair of circumferentially aligned first and second high pressure balancing grooves on either side of the high pressure ports and a pair of circumferentially aligned first and second low pressure balancing grooves on either side of the low pressure ports. The control member is formed with preferably straight diametrical ducts connecting the first and second high pressure balancing grooves with the first and second low pressure balancing grooves located on the same side of the high pressure and low pressure ports, respectively. The high pressure balancing grooves and the low pressure balancing grooves are filled, respectively, with high pressure fluid and low pressure fluid from the high pressure and low pressure ports, respectively, through the gap between the inner surface of the cylinder block and the outer surface of the control member so that the pressure fluid in the balancing grooves substantially centers the cylinder block on the control member.

United States Patent [19] Bosch [11] 1 3,810,418 [451 May 14,1974

[ CENTER RING ARRANGEMENT FOR A RADIAL PISTON MACHINE [75] Inventor: Paul Bosch, Ludwigsburg, Germany [73] Assignee: Robert Bosch, GmbH, Stuttgart,

Germany [22] Filed: June 27, I973 21] Appl. No.: 373,961

Great Britain 9l/498 Primary Ex'aminen-William L. Freeh 5 7] ABSTRACT The rotary cylinder block of a radial piston machine surrounds a control member whose outer surface has high pressure ports and low pressure ports communicating with the cylinders during rotation. The outer cylindrical surface of the control member also has a pair of circumferentially aligned first and second high pressure balancing grooves on either side of the high pressure ports and a pair of circumferentially aligned first and second low pressure balancing grooves on either side of the low pressure ports. The control member is formed with preferably straight diametrical ducts connecting the first and second high pressure balancing grooves with the first and second low pressure balancing grooves located on the same side of the high pressure and low pressure ports, respectively.

The high pressure balancing grooves and the low pressure balancing grooves are filled, respectively, with high pressure fluid and low pressure fluid from the high pressure and low pressure ports, respectively, through the gap between the inner surface of the cylinder block and the outer surface of the control member so that the pressure fluid in the balancing grooves substantially centers the cylinder block on the control member.

10 Claims, 5 Drawing Figures BACKGROUND OF THE INVENTION The present invention relates to a radial piston machine, pump or hydraulic motor, with a rotary cylinder block in whose radially arranged cylinder bores, pistons are guided whose outer ends are in sliding engagement with an eccentric cam ring. The cylinder block surrounds the outer cylindrical surface of a stationary control member which has two diametrically opposite circumferentially elongated low pressure and high pressure ports separated by sealing surface portions of the outer cylindrical surface of the control member.

A machine of this type is disclosed in the German OSl,45 3,628. In order to equalize the varying loads act- I ing on the control member due to the pressure differential between the high pressure fluid and the low pressure fluid in the machine, on both sides of the low pressure ports in the control member, a pressure area extending over an angle of substantially 160 is provided. The pressure areas are connected by bores with the high pressure port by check valves closing toward the high pressure side of the machine. The forces acting in the pressure areas are to be so great that the effect of the pressureon the high pressure side of the machine on the bearing of the cylinder block is substantially compensated. Due to the fact that the pressure areas are directly connected with the high pressure side, .and that continuously pressure fluid flows from the high pressure side, the machine has great leakage losses,

which is particularly noticeable when there is a comparatively great play provided between the inner bore of the cylinder block and the control member. A comparativelylarge play is required because of certain operational conditions, the control member with the high pressure and low pressure ports, assumes a higher temperature than the cylinder block, whereby the play is reduced.

SUMMARY OF THE INVENTION.

It is an object of the invention to provide a radial piston machine of compact and simple construction, in which the rotary cylinder block is in close contact with the control member on the high pressure side of the machine, Without increasing the leakage losses.

Another object of the invention is to center the cylinder block on the control member.

With these objects in view, two pressure areas are provided on either side of the high pressure and low pressure ports, of which always two pressure areas, associated with twodifferent ports, are connected with each other, while the inflow and outflow of the pressure fluid to and from the pressure areas takes place through the gap between the cylinder block and the control member.

This has the advantage that, in a radial piston machine, the cylinder block abuts the control member in a radial plane of symmetry, using the leakage flow which is present in any event, without increasing the leakage flow. I

It is particularly advantageous when the pressure areas with which the low pressure port is connected,

have a greater axial width than the pressure areas which are connected with the high pressure port.

The novel features which are considered as characteristic for the invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWING view illustrating the distribution of forces in the ma-' chine; and

FIG. 5 is a fragmentary view illustrating a modified construction of the outer cylindrical surface of the control member.

DESCRIPTION OF THE PREFERRED EMBODIMENTS A, radial piston machine illustrated in the drawing, which may operate as a pump or hydraulic motor, has a housing 1 closed by a cover plate 2 which has a cylindrical flange 2a and an arresting screw 2b for securing the control member 3 to the housing. A high pressure conduit 4, and a low pressure conduit extend in axial direction in the control member 3, and are respectively connected with highpressure and low pressure ports 6 and 7 which extend in circumferential direction over almost half of the circumference of control member 3 and the outer cylindrical surface 3a thereof, so that narrow sealing portions 8 and 9 remain, as best seen in FIGS. 1 and 3.

It is assumed that the radial piston machine operates as a pump, and that control port 6 communicates with low pressure fluid, and control port 7 communicates with high pressure fluid. The circumferential width of the sealing surface portions 8 and '9 between the low pressure and high pressure ports 6 and 7, are dimensioned to prevent direct communication between the low pressure and high pressure ports 6,7.

On either side of the control ports 6, 7, two balancing grooves 10 to 17 are arranged. A pair of circumferentially aligned first and second high pressure balancing grooves 14, 15 and l6, 17 are provided on either side of the high pressure port 7, and a pair of circumferentially aligned first and second low pressure balancing grooves 10, 11 and '12, 13 are provided on either side of the low pressure port. The rectangular outline of the balancing grooves 10-17 is best seen in FIG. 3, and the respective balancing grooves are so closely spaced in axial direction from the ports-6 and 7, that between the ports 6 and 7 and the balancing grooves, remains a sealing strip l8, 19 which extend around the entire circumfe rence in the'outer cylindrical surface 3a of control member 3.

The balancing grooves 10, ll, 12 and 13, whichare arranged at opposite sides of the low pressure port 6, have a greater axial width than the balancing grooves 14, 15, 16, 17 which are arranged on opposite sides on the high pressure port 7. Pairs of high pressure and low pressure grooves follow each other in a circumferential direction on either side of the low pressure ports and high pressure ports 6 and 7. Diammetrically disposed high pressure and low pressure balancing grooves, are connected by transverse ducts or bores 20-23, respectively. The position of the straight ducts 20-23 is best seen in FIG. 2, but FIG. 3 shows schematically the ducts 10-23 connecting the balancing grooves as follows: Balancing groove 10 is connected with balancing groove 14 by duct 20, balancing groove 12 is connected with balancing groove 16 by duct 22, balancing groove 11 is connected with balancing groove by duct 21 and balancing groove 13 is connected with balancing groove 17 by duct 23.

Fluid conduits supplying or discharging fluid from the balancing grooves 10-17, are not provided, and the flow of fluid to and from the balancing grooves 10-17 takes places only through the gap between the outer cylindrical surface 3a of control member 3 and the inner cylindrical surface 24a of the cylinder block 24.

The cylinder block 24 is mounted in a bearing 25 supported by housing 1, and surrounds the control member 3. A shaft 26, connected with the cylinder block 24, can be used as a vdrive shaft when the machine is operated as a pump, and as output shaft when the machine is operated as a motor. In the cylinder block 24, a set of angularly spaced cylinder bores 27 is provided, of which only one cylinder bore 27 is shown. Pistons 28 are guided in the cylinder bores 27 in sliding and sealing contact, and the working chambers in the cylinder bores 27 are connected by cylinder ports 29 with the high pressure port 7 or the low pressure port 6, depending on the angular position of the cylinder block 24.

Each piston 28 is connected by a ball joint 28a with a part circular slide shoe 30 which slides on the inner cylindrical surface 31 of an eccentric cam ring 31 so that the pistons 28 are reciprocated in radial direction in the cylinder bores 27 during rotation of cylinder block 24 by the drive shaft 26. Between the rotation,

the cylinder ports 29 successively communicate with the ports 6 and 7, and when a piston 28 is in the inner dead center position, fluid is discharged through high pressure port 7 and high pressure conduit 5.

The function of the pressure areas defined by the pressure grooves 10-17 will now be explained with reference to the schematic FIG. 4 in which the gap between the outer surface 3a.of the control member 3 and the inner surface 24a of the cylinder block 24 is shown with exaggerated radial thickness. Balancing grooves 10, ll, 14 and 15 which function as described above,

are shown in FIG. 4, and since the balancing grooves 10-15 are axially' aligned with the balancing grooves 12-17, respectively, they are not visible, but function as described above in the same manner as the balancing grooves 10-15.

It is now assumed that the cylinder block 24 rotates in the direction of the arrow 32. As mentioned above,

the flow of the pressure fluid to and from the balancing grooves takes place through the narrow gap 40 between the surfaces 24 and 3a. Since the gap does not have the same radial height along the entire circumference of the control member 3, different throttling flow resistances result for the pressure fluid flowing to the balancing grooves. The fluid pressures acting at the balancing grooves and on the marginal face portions surrounding the same, depend on the throttle resistances acting'on the fluid flowing to and from the balancing grooves, respectively, and consequently depend on the radial thickness of gap 40 upstream and downstream the balancing grooves.\

A force F and a force F,, act on the rotating cylinder block 24. The force F is produced by the high pressure port 7, and has the effect to urge the cylinder block 24 away from the control member. The force F, is the resultant of all forces produced by the pistons 28 whose cylinders are connected with the high pressure port 7, and acting on the cylinder bores 27. The magnitude of the force F, depends on the pressure, and the selected stroke length of the piston 28, and the force F, urges the cylinder block 24, downward as viewed in FIG. 4, toward the control member 3. When the forces F, and F are not controlled by balancing grooves, the radial height of the gap 40 in the region of the high pressure port 7 would be very great, particularly if the average force F, is very small which would cause great leakage losses.

When the cylinder block 24 assumes the position shown in FIG. 4 in an exaggerated manner, the pressure in the balancing groove 15, and due to duct 2-1, the

pressure in the balancing groove 11 is greater than in the balancing grooves 14 and 10 which are connected by the duct 20 with each other. This is due to the fact thatthe flow toward the balancing groove 14 is throttled to a far greater extent than the flow to balancing groove 15 due to the small thickness of the gap 40 between the control member 3 and the cylinder block 24. Furthermore, the resistance against fluid flowing out of the balancing groove 10 is smaller than the resistance against flowing out downstream of the balancing groove 11, because the gap 40 between the control member surface 3a and the cylinder block surface 24, is higher in radial direction in the region of the balancing groove 10 than in the region of the balancing groove 11.

The pressure forces produced at the balancing grooves 10-17 result in the resultant F shown in FIG. 4. The force F urges the cylinder block 24 against the pressure side of control member 3, since the balancing grooves 10-13 produce a greater pressure than the balancing grooves 14-17.

The vector sum of the forces F, and F, results in a resultant'force R which urges the cylinder block 24 in the desireddirection, that is upward in FIG. 4. As a result of the displacement of the cylinder block, the pressure at the balancing grooves 14 and 10 rises, and the pressure in the balancing grooves 15 and 11 drops. This is continued until the forces F F and F balance each other, which means that the force R has become zero. When this takes place, the control member 3 is at least substantially centered within the cylindrical inner surface 24a of cylinder block 24.

By a variation .of the axial width of the high pressure and low pressure ports 7 and 6, the magnitude of the force F,,, and by the dimensions of the balancing grooves 10-17, the magnitude and angular position of the force F resulting therefrom, can be selected through certain relative positions of the cylinder block 24 and the control member 3. Control member 3, modified in this manner, is illustrated in FIG. 5. In order to maintain the excess forces of balancing grooves 10 and 11 great, the flow resistance upstream of the balancing grooves 14 and 15 is made small by selecting narrow sealing strips 18' and 19'.

If the position of the balancing grooves 10-17 on control member 3 is angularly displaced a predetermined angle in counterclockwise direction, as viewed in FIGS. 2 and 4, more favorable positions of control member 3 can be obtained for certain regions of the eccentricity of the camming ring 31, than in the symmetrical arrangement of FIG. 4.

Generally speaking, a radial piston machine according to the invention comprises a stationary control member 3 having an outer cylindrical surface 3a having an axis and being formed with circumferentially aligned diammetrical disposed high pressure and low pressure ports 7, 6; rotor means 24, 27, 28 mounted for rotation about the axis and including a cylinder block 24 having an inner cylindrical surface 24a surrounding the outer cylindrical surface 3a and forming a gap 40 therewith, the cylinder block 24 having radial cylinder bores 27 successively passing over the high pressure and 'low pressure ports 7, 6 during rotation of the rotor means, and pistons 28 in said cylinder bores 27; cam ring means 31 having an endless inner surface eccentric to said axis surrounding said cylinder block 24 and being slidingly engaged by the radially oute'r ends 30 of said pistons 28 for reciprocating said piston in said cylinder bores 27, said outer cylindrical surface 3a of said control member 3 having a pair of circumferentially aligned first and second high pressure balancing grooves l4, l5 and l6, 17 on either side of the high pressure port 7, and a pair of circumferentially aligned first and second low pressure balancing grooves 10, 1] and l2, 13 on either side of said low pressure port. The control member 3 is formed with ducts -24 connecting the first and second high pressure balancing grooves l4, l5 and l6, 17 with the first and second low pressure balancing grooves l0, l1 and 12, 13 located on the same side of the high pressure and low pressure ports 7, 6, respectively. The first and second high pressure balancing grooves 14-17 and the first and second low pressure balancing groove 10-13 are filled, respectively, with high pressure fluid and low pressure fluid from the high pressure and low pressure ports 7, 6, respectively, through the gap 40 between said inner surface 24a of the cylinder block 24 and the outer surface 30 of the control member 3 whereby the cylinder block 24 is substantially centered on the control member 3.

lt will be understod that each of the elements described above, or two or more together, may also find a useful application in other types of radial piston machines differing from the types described above.

While the invention has been illustrated .and described as embodied in an arrangement for centering the cylinder block ofa radial piston machine on a control member having high pressure and low pressure ports, it is not intended to be limited to the details shown, since various modifications and structural changes may be made without departing in any way from the spirit of the present invention.

Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can by applying current knowledge readily adapt it for various applications without omitting features that, from the standpoint of prior art fairly constitute essential characteristics of the generic or specific aspects of this invention and, therefore, such adaptations should and are intended to be comprehended within the meaning and range of equivalence of the following claims.

What is claimed as new and desired to be protected by Letters Patent is set forth in the appended claims.

I claim:

l. Centering arrangement for a radial piston machine, comprising a stationary control member having an outer cylindrical surface having an axis and being formed with circumferentially aligned diametrically disposed high pressure and low pressure ports; rotor means mounted for rotation about said axis and including a cylinder block having an inner cylindrical surface surrounding said outer cylindrical surface and forming a gap therewith, said cylinder block having radial cylinder bores successively passing over said high pressure and low pressure ports during rotation of said rotor means, and pistons in said cylinder bores; cam ring means having an endless inner surface eccentric to said axis surrounding said cylinder block and being slidingly engaged by the radially outer ends of said pistons for reciprocating said pistons in said cylinder bores, said outer cylinderical surface of said control member having a pair of circumferentially aligned first and second high pressure balancing grooves on either-side of said high pressure port, and a pair of circumferentially aligned first and second low pressure balancing grooves on either side of said low pressure port, said control member being formed with ducts connecting the first and second high pressure balancing grooves with said first and second low pressure balancing grooves located on the same side of said high pressure and low pressure ports, respectively, said first andsecond high pressure balancing grooves and said first and second low pressure balancing grooves being filled, respectively, with high pressure fluid and low pressure-fluid from said high pressure and low pressure ports, respectively, through said gap between said inner surface of said cylinder block and said outer surface of said control member wherebysaid cylinder block is substantially centered on said control member.

2. Centering arrangement as claimed in claim 1 wherein said pairs of low pressure balancing grooves located on opposite sides of said low pressure port, are wider in axial direction than said pairs of high pressure balancing grooves located on opposite sides of said high pressure port.

3. Centering arrangement as claimed in claim 1 wherein the ends of said first and second balancing grooves of each pair of balancing grooves located on one side of said ports are aligned in axial direction with the ends of the first and second balancing grooves of a corresponding pair located on the other side of said ports. I

4. Centering arrangement as claimed in claim 1 wherein said high pressure and low pressure ports have the same circumferential length, and have adjacent ends spaced the same distance in circumferential direction of said outer cylindrical surface; and wherein said high pressure and low pressure balancing grooves of each pair have substantially half said circumferential length of said high pressure and low pressure ports.

5. Centering arrangement as claimed in claim 1 wherein said high pressure balancing grooves of each pair of high pressure balancing grooves are spaced from said high pressure port a smaller distance in axial direction than said low pressure balancing grooves of each pair of low pressure balancing grooves are spaced from said low pressure port in axial direction so that the sealing surface portions of said outer cylindrical surface between said high pressure balancing grooves and said high pressure port are narrower than the sealing surface'portions of said outer cylindrical surface between said low pressure balancing grooves and said low pressure port.

6. Centering arrangement as claimed in claim 1 wherein said pairs of high pressure and low pressure balancing grooves are symmetrically arranged on said cylindrical outer surface in relation to said high pressure and low pressure ports.

7. Centering arrangement as claimed in claim 1 wherein said balancing grooves are staggered in circumferential direction in relation to said high pressure and low pressure ports.

10. Centering arrangement as claimed in claim 9 wherein the adjacent ends of said first and second balancing grooves of each pair of balancing grooves are spaced the same circumferential distance. 

1. Centering arrangement for a radial piston machine, comprising a stationary control member having an outer cylindrical surface having an axis and being formed with circumferentially aligned diametrically disposed high pressure and low pressure ports; rotor means mounted for rotation about said axis and including a cylinder block having an inner cylindrical surface surrounding said outer cylindrical surface and forming a gap therewith, said cylinder block having radial cylinder bores successively passing over said high pressure and low pressure ports during rotation of said rotor means, and pistons in said cylinder bores; cam ring means having an endless inner surface eccentric to said axis surrounding said cylinder block and being slidingly engaged by the radially outer ends of said pistons for reciprocating said pistons in said cylinder bores, said outer cylinderical surface of said control member having a pair of circumferentially aligned first and second high pressure balancing grooves on either side of said high pressure port, and a pair of circumferentially aligned first and second low presSure balancing grooves on either side of said low pressure port, said control member being formed with ducts connecting the first and second high pressure balancing grooves with said first and second low pressure balancing grooves located on the same side of said high pressure and low pressure ports, respectively, said first and second high pressure balancing grooves and said first and second low pressure balancing grooves being filled, respectively, with high pressure fluid and low pressure fluid from said high pressure and low pressure ports, respectively, through said gap between said inner surface of said cylinder block and said outer surface of said control member whereby said cylinder block is substantially centered on said control member.
 2. Centering arrangement as claimed in claim 1 wherein said pairs of low pressure balancing grooves located on opposite sides of said low pressure port, are wider in axial direction than said pairs of high pressure balancing grooves located on opposite sides of said high pressure port.
 3. Centering arrangement as claimed in claim 1 wherein the ends of said first and second balancing grooves of each pair of balancing grooves located on one side of said ports are aligned in axial direction with the ends of the first and second balancing grooves of a corresponding pair located on the other side of said ports.
 4. Centering arrangement as claimed in claim 1 wherein said high pressure and low pressure ports have the same circumferential length, and have adjacent ends spaced the same distance in circumferential direction of said outer cylindrical surface; and wherein said high pressure and low pressure balancing grooves of each pair have substantially half said circumferential length of said high pressure and low pressure ports.
 5. Centering arrangement as claimed in claim 1 wherein said high pressure balancing grooves of each pair of high pressure balancing grooves are spaced from said high pressure port a smaller distance in axial direction than said low pressure balancing grooves of each pair of low pressure balancing grooves are spaced from said low pressure port in axial direction so that the sealing surface portions of said outer cylindrical surface between said high pressure balancing grooves and said high pressure port are narrower than the sealing surface portions of said outer cylindrical surface between said low pressure balancing grooves and said low pressure port.
 6. Centering arrangement as claimed in claim 1 wherein said pairs of high pressure and low pressure balancing grooves are symmetrically arranged on said cylindrical outer surface in relation to said high pressure and low pressure ports.
 7. Centering arrangement as claimed in claim 1 wherein said balancing grooves are staggered in circumferential direction in relation to said high pressure and low pressure ports.
 8. Centering arrangement as claimed in claim 1 wherein said ducts are straight and extend diametrically through said control member for connecting high pressure and low pressure balancing grooves diametrically disposed in said outer cylindrical surface of said control member.
 9. Centering arrangement as claimed in claim 1 wherein all said high pressure and low pressure balancing grooves have the same circumferential extension on said outer cylindrical surface of said control member.
 10. Centering arrangement as claimed in claim 9 wherein the adjacent ends of said first and second balancing grooves of each pair of balancing grooves are spaced the same circumferential distance. 